Liquid running into the electrical parts is one of the parameters affecting the lifetime and operability of electronic instruments, such as hearing aids. Penetration of liquids—e.g. water or sweat running from the scalp into e.g. electrical contacts will typically result in malfunctions of the hearing instrument.
U.S. Pat. No. 3,195,358 discloses weather-tight instrument housings and assemblies for switches, potentiometers and the like. The modular unit of the instrument housings includes a basic housing portion having substantially parallel front and back sides and a generally cylindrical cavity for containing adjustable electrical mechanism formed in the back surface.
U.S. Pat. No. 4,081,782 discloses a potentiometer and switch combination including a rotatable control cap positioned over a potentiometer body to form a housing. The cap is provided with an annular flange which abuts an annular shoulder on the body, either the flange or the shoulder being formed from stiffly flexible, resilient material. The body holds the cap in place by means of a post having a chevron at its upper end which mates with a recess in the cap. The cap is positioned to deform the stiffly flexible, resilient material into frictional sealing relation with its abutting member and thereby seal the interior of the housing. Rotating the cap moves a blocking member out from between the contacts, permitting them to close, and also causes a spring detent to snap against the blocking member and give the operator a positive switch feel.
It is a disadvantage of the inventions disclosed in the above-mentioned references that the member to be used in activating the device is not encapsulated, or at least partly encapsulated, in a housing—see e.g. the rotatably mounted member 30 in FIG. 2 of U.S. Pat. No. 3,195,358. This non-encapsulated member makes it rather difficult to integrate the device of U.S. Pat. No. 3,195,358 in an outer wall of another small device/apparatus, such as a hearing aid.